The present invention relates generally to a system for the spray application of epoxy materials. More specifically, the present invention is directed to a method and system for preheating the various components of epoxy materials prior to their being mixed in order to reduce their viscosity thereby facilitating spray application thereof.
Generally, epoxy coatings are well known in the art and due to their exceptional durability and structural properties epoxy based protective coatings have gained commercial acceptance as protective and decorative coatings for use on a wide variety of materials. For example, epoxy based protective coatings represent one of the most widely used methods of corrosion control. They are used to provide long term protection of steel, concrete, aluminum and other structures under a broad range of corrosive conditions, extending from atmospheric exposure to full immersion in highly corrosive environments. Further, epoxy coatings are readily available and are easily applied by a variety of methods including spraying, rolling and brushing. They adhere well to steel, concrete and other substrates, have low moisture vapor transmission rates and act as barriers to water, chloride and sulfate ion ingress, provide excellent corrosion protection under a variety of atmospheric exposure conditions and have good resistance to many chemicals and solvents. As a result, numerous industries including maintenance, marine, construction, architectural, aircraft and product finishing have adopted broad usage of epoxy coating materials.
The most common material utilized in the epoxy coating industry today is a multi-part epoxy material. In general the epoxy includes a first base resin matrix and at least a second catalyst or hardener, although other components such as a pigment agent or an aggregate component may also be added. While the two parts remain separate, they remain in liquid form. After the two parts are mixed together, they begin a curing process that is typically triggered by exposure to heat, humidity or a ultra-violet light source, whereby the mixed material quickly begins to solidify. The resin base and the catalyst are typically highly viscous in consistency and when mixed, generally having a paste like consistency.
The difficulty found in the prior art is that while epoxy has highly desirable characteristics as a finished coating, the preferred method of application is spray application. When attempting to spray apply an epoxy, two drawbacks are encountered. First, the material cannot be mixed in large batches prior to application because of the short pot life of the material. Accordingly, it must be mixed on an as needed basis immediately prior to spray application. Second, the naturally viscous consistency of the mixed epoxy material is not well suited for spray application. To thin the epoxy to the consistency required for typical prior art spray application, the epoxy must be loaded with a large percent by volume of solvent. Such a solvent typically contains high level of volatile organic compounds (VOC) whose primary function is to lower viscosity thereby providing a consistency suitable for spray application with conventional air, airless and electrostatic spray equipment. The addition of the solvent to the epoxy coating material in turn greatly increases the VOC content of the epoxy coating material and reduces the build thickness of the finished and cured coating.
In view of the above, the problem with spray application of epoxy coating materials becomes two fold. First, there is a growing emphasis on compliance with government environmental and health hazard regulations, which in turn has prompted coating material manufacturers and end users to evaluate new coating technologies. The Clean Air Act sets limits on both the type and amount of VOC content found in coating materials and has resulted in research directed to higher solids, solventless and waterborne protective coating systems. As a result of such research, the newer epoxy materials are either highly viscous resulting in a poor quality finish when spray applied or too thin to produce the type of high build coating that is normally expected from spray applied epoxy coatings.
While many processes and techniques have been proposed in the prior for the spray application of epoxy coating materials to substrates, prior art spray processes are directed to the reduction of material viscosity through the use of solvents. In most cases, such spray operations operate with materials having a low viscosity on the order of 100 poise and utilize a relatively low application pressure on the order of no more than about 100 psi.
Therefore, there is a need for a system and method of spray application of high molecular weight, highly viscous polymeric thermally cured materials at elevated temperature. There is a further need for a system and method of applying epoxy coating materials that eliminates or reduces the need for solvent loading while also providing a mixed epoxy product that has a consistency that is suitable for spray application. There is still a further need for a system for spray applying an epoxy material that is capable of continuous duty wherein a low viscosity epoxy can be spray applied without a high level of equipment down time or recycling time. Simply stated, the art is devoid of any proven technique for spraying high molecular weight epoxy coating materials of this character.